The principal objective is to study the mechanisms by which simple neural networks process information with particular emphasis on mechanisms of learning. The nervous system of Hermissenda crassicornis has proven to be a good model for information processing at several levels: sensory transduction by photoreceptors and hair cells, analysis of synaptic circuitry, changes in synaptic circuitry produced by conditioning paradigms administered to intact animals, as well as to isolated nervous systems, membrane properties modified by conditioning, identification of critical developmental stages for the neural networks of interest, as well as stages critical for learning. Techniques employed thus far to pursue these questions include simultaneous intracellular recording from multiple neural elements, paired stimulation of the visual and vestibular pathways using a rotating table, iontophoresis of fluorescent dyes and electron dense materials, electron microscopy, automated behavioral monitoring of intact Hermissenda, voltage clamp of identified neural elements. Other methods include mariculture, subcellular fractionation, protein phosphorylation analysis, uptake of neurotransmitter precursors, phosphoprotein characterization and purification, and immunologic protein identification. Patch clamp of membrane fragments of identified neurons is also being combined with enzymatic regulation of specific channels changed by learning to determine molecular mechanisms for encoding associatively learned information. Analogous protocols are also conducted with brain slices from neuronal aggregates which mediate classical conditioning of the rabbit nictitating membrane.